Ultrasonic position sensor for measuring movement of an object

Abstract

A position sensor for measuring the distance from a first position to a second position. The sensor may include an elastic wave generator, an acoustical path over which the elastic wave passes, and a transducer to which the wave passes. A measurement loop includes the acoustical path, and has electrical and optical elements. The electrical elements may compare the phases of the transducer signals from which the change in position between the first and second positions are determined. Alternatively, the measurement loop may comprise a feedback loop to produce oscillations and an output frequency. A frequency counter is included in the feedback loop to measure frequency.

What is claimed is: 
     
       1. A position sensor for measuring the distance that an object moves from a first position to a second position, comprising: a membrane having an acoustical path over which Lamb waves may propagate,   a transducer means coupled to said membrane for generating Lamb waves in said membrane,   a light source spaced from said membrane for producing a light beam that can be shined onto and reflected from the surface of said membrane,   a feedback loop, including said acoustical path, said transducer means, optical detector means for producing an output voltage when illuminated by reflected light from said membrane and an amplifier for amplifying said output voltage with sufficient gain to overcome transducer means losses, attenuations in said acoustical path and losses in said optical detector means, an amplified output voltage being applied to said transducer means to generate the Lamb waves and said feedback loop producing self-oscillations at an output frequency and an output voltage, and   a frequency counter for measuring the difference in output frequency at the first and second positions of said object to provide a measure of the distance between said first and second positions.   
     
     
       2. A position sensor, comprising: an electrical generating transducer for propagating Lamb waves on a membrane and a light source for directing a light beam toward said membrane,   a detector for detecting a reflected light beam from said membrane once per cycle of a Lamb wave propagating in said membrane and for producing an amplitude-modulated current output,   an amplifier for producing an amplified output from the detector, and   feedback means for feeding said amplified output to said generating transducer.   
     
     
       3. A position sensor for measuring the distance from a first position to a second position of an object, comprising: a membrane having an acoustical path over which Lamb waves may propagate,   a transducer for generating Lamb waves in said membrane,   a light source spaced from said membrane for producing a light beam that can be directed to and reflected from a surface of said membrane to provide an optical transducer for receiving Lamb waves propagating in said membrane,   an optical detector for producing a signal when illuminated by reflected light from said membrane,   a feedback element connected to said optical detector and to said transducer to generate the elastic waves, and to form a feedback loop including said optical transducer and said optical detector for producing oscillations at an output frequency and voltage, and   a frequency counter for measuring the difference in output frequency at the first and second positions of said object to provide a measure of the distance between said first and second positions.   
     
     
       4. A position sensor, comprising a light source for generating a light beam,   a membrane toward which said beam is directed,   electrical means for propagating Lamb waves on said membrane,   a photodetector having current output,   an amplifier therefore producing an amplified output of the current from said detector fed to said electrical means,   optical means directing onto said photodetector both a portion of said light beam and an optical beam reflected from the elastic wave propagation path, thereby to produce by optical mixing a frequency-modulated current output from the photodetector, and   feedback means for feeding said amplified output to said generating transducer.